Why can't Matlab do the factorial of a non-integer number?

Hi,

I tried using the factorial function on a number with decimals and got the following error: N must be an array of real non-negative integers.

Is there an alternative so that it can calculate the factorial of a number with decimals like Excel does?

Thanks for your time

Answer 1

[Davide Masiello]

MatLab 'factorial' is coded so to work with integers only.

The generalization of a factorial is the Γ function, which is

and the relation with the factorial is

MatLab implements the Γ function. Therefore, to compute the factorial of 1.5 you can write

gamma(2.5)

Which yields 1.3293, the correct answer.

Answer 2

[David Hill]

Use the gamma function.

gamma(1.3);

Answer 3

[DGM]

See the Gamma function

https://en.wikipedia.org/wiki/Gamma_function

Or in MATLAB, gamma().

Note that if you're trying to replicate the behavior of factorial, the input is offset by 1:

factorial([2 3 4])

ans = 1×3

2 6 24

gamma([2 2.5 3 3.2 3.6 4])

ans = 1×6

1.0000 1.3293 2.0000 2.4240 3.7170 6.0000

gamma([2 2.5 3 3.2 3.6 4]+1) % offset by 1

ans = 1×6

2.0000 3.3234 6.0000 7.7567 13.3813 24.0000